In conventional stereo audio coding, possible coding schemes include parametric stereo coding techniques which are used in low bitrate applications. At intermediate rates, Left/Right (L/R) or Mid/Side (M/S) waveform stereo coding is often used. The existing distribution formats and the associated coding techniques may be improved from the point of view of their bandwidth efficiency, especially in applications with a bitrate in between the low bitrate and the intermediate bitrate.
An attempt to improve the efficiency of the audio distribution in a stereo audio system is made in the Unified Speech and Audio Coding (USAC) standard. The USAC standard introduces a low bandwidth waveform-coding based stereo coding in combination with parametric stereo coding techniques. However, the solution proposed by USAC uses the parametric stereo parameters to guide the stereo coding in the modified discrete cosine transform (MDCT) domain in order to do something more efficient than plain M/S or UR coding. The drawback with the solution is that it may be difficult to get the best out of the low bandwidth waveform based stereo coding in the MDCT domain based on parametric stereo parameters extracted and calculated in a Quadrature Mirror Filters (QMF) domain.
In view of the above, further improvement may be needed to solve or at least reduce one or several of the drawbacks discussed above.
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